735 


Lantern Slide Lecture 


of 

Steam Turbines 



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LANTERN SLIDES. 

KW 


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USE OF STEREOPTICON 


A direct- current arc light gives best results. Connect terminals so that the 
brightest carbon will point toward lens. Alternating current can be used with 
proper holders for carbons. Calcium light is satisfactory. Acetylene is not so 
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not absolutely necessary if due care is exercised. 




COPYRIGHTED 1917 


BY THE 

NATIONAL ASSOCIATION OF STATIONARY ENGINEERS 


JUN II 1917 

©CI.A462939 
^ivS) j ' 


V. 


jgSteam ^ttcbriues 


Both the steam engine and the steam turbine are devices by which 
the heat energy in steam is transformed into work. The difference 
between them lies in the way in which this is done. In the steam 
engine, the pressure of the steam is used to drive a piston back and 
forth, and this to-and-fro motion is converted into a rotary motion 
of the crankshaft; but in the steam turbine, the turning is not cau¬ 
sed by the pressure of the steam, as in the engine. Instead, the 
energy in jets of steam moving at high velocity is used to perform 
the work of turning the shaft. 

Every steam turbine must have a stationar) part and a movable 
part, called the rotor. The rotor is the part that is fixed to the shaft 
and it turns inside the stationary part, the shaft being held in suit¬ 
able bearings at the ends. This shaft may be horizontal, in which 
case the turbine is called a horizontal turbine; or it may stand on one 
end, in which case the turbine is known as a vertical turbine. 



T-l 

The easiest way to understand how the steam turbine operates is 
to study first the action of the Pelton water wheel, shown in this 


3 




view. The wheel is mounted on a shaft that runs in bearings' 
and around the edge ^of the wheel are fastened a number of 
buckets, each shaped something like the letter B; that is, each 
buckethas two rounded pockets that meet along a sharp edge at the 
middle. Squarely in frcnt of this sharp edge, and in line with the 
bottom of the wheel, is a pipe whose end is tapered to a nozzle, and 
this nozzle is bolted firmly to the foundation. The water that runs 
the wheel is led to the nozzle Ihrough a pipe not shown, but that is 
bolted, to the flange of the heavy valve. The valve is used to regu¬ 
late the quantity of water flowing through the nozzle. 

When the valve is opened, water flows through the nozzle, 
comes out at the small end in a solid stream, and strikes the bucket 
directly in front of it. Any one who has ever used a hose for sprinkling 
knows that the stream of water has power to wash away rubbish, 
and even move such heavy objects as stones. So, in this case, the 
water strikes the bucket and moves it in the direction in which the 
stream is moving. This causes the wheel to turn, and as soon as lhat 
happens, the next bucket comes in line with the nozzle and is acted 
on by the jet of water, making the wheel turn faster, and soon the 
wheel is rotating at a high speed, the water striking each bucket as 
it comes in the path of the jet. By running a belt over the pulley 
on the farther end of the wheel shaft, the wheel can be made to 
drive machinery or do other work. 

Now, in this water wheel, the water is able to cause the buckets 
to move because of the speed, or velocity,, with which it is moving 
when it leaves the end of the nozzle. The greater this speed, the 
harder it will strike the buckets and the greater will be the speed at 
which the wheel will turn. 

Where does the water get its velocity? . What causes the jet to 
leave the nozzle at such a high speed? Simply this—-—the pressure 
due to the height of the dam or reservoir from which the water 
flows to the nozzle. To illustrate this, let us suppose that the sur¬ 
face of the water in the reservoir is 100 feet above the nozzle. 
When the valve is closed, the pressure at Ihe valve, due to this 100 
feet of water, is about 43 pounds per square inch. Now, if the valve 
is opened, this pressure acts so as to force the water out, and the jet 
coming from the nozzle has a speed of about 80 feet per second. In 
other words, the pressure due to the height of the water is used to 
give the stream a high velocity. 

While the water was held back by the valve, it had energy due 
to its pressure, or potential energy; but as soon as the valve was 


4 



opened, the pressure energy was converted into kinetic energy, or 
energy of motion. This conversion of potential energy to kinetic 
energy is exactly what takes place in the steam turbine and so en¬ 
ables the steam to drive the rotating part of the turbine. While 
the steam is confined in the boiler or in the steam pipe, it has 
potential energy because of its pressure. If it is admitted to an engine 
cylinder, this pressure energy can be converted into motion. But 
if the steam is allowed to escape through a hole in the pipe or through 
a nozzle attached to the pipe, the potential energy will be converted 
into kinetic energy, because the steam will come out with an ex¬ 
ceedingly great velocity. If, then, a wheel with suitable blades is 
placed in the path of the jet of steam, the wheel will be turned, 
exactly as the stream of water turned the Pelton wheel. 

The only difference between the two cases is that the water does 
not expand, or increase in volume, to any extent, whereas steam 
must expand in order to convert its potential energy into kinetic 
energy. 



T-2 

The principle of action of the steam turbine may be explained 
very readily by this view, which illustrates the De Laval single- 
stage impulse turbine, and is used by this company as their trade 
mark. It consists of a wheel or disk mounted on a comparatively 
light shaft and carrying a row of buckets or vanes around its outer 
edge. These vanes are moon-shaped in cross-section, as may be 
seen at the point where the outer band is cut away. The steam 
that runs the turbine is admitted through four nozzles placed at 


5 





equal distances around the wheel; but instead of being set squarely 
opposite the edge of the wheel, as in the Pelton water wheel, the 
nozzles are set along one side, and are inclined at an angle of about 
20 degrees away from the wheel. 

The four nozzles are exactly alike, and the shape of the passages 
through them is like that shown in black in the front nozzle in the 
picture. The steam is led to the outer end of each nozzle by a pipe. 
In passing through the nozzle the steam expands and its potential 
energy is converted into kinetic energy. The result is that the 
steam comes out of the nozzle at a very great velocity. When it 
does so, it strikes the curved buckets and exerts a force on them that 
causes the wheel to turn, thus bringing other buckets in line with the 
end of the nozzle. The steam then escapes at the opposite side of 
the wheel, in a direction opposite to that which it had when it left 
the nozzle. 

Do you wonder how anything so light as steam has the power to 
turn a heavy turbine wheel? If you do, it is necessary for you to 
understand something about kinetic energy, or the energy of motion. 
The amount of kinetic energy in a body, which is a measure of the 
work it can do, depends on two things—the weight of the body and 
the speed with which it is moving. If the weight of the body is in¬ 
creased, the kinetic energy increases at the same rate; that is, 
doubling the weight doubles the kinetic energy. But changing the 
speed acts in a different way. If the speed is made twice as great, 
or doubled, the kinetic energy is made four times as great, and if the 
speed is made ten times as great, the kinetic energy becomes 100 
times as great as before; that is, the kinetic energy increases as the 
square of the velocity. 

In the case of a water wheel, the water is very heavy, as compared 
with an equal volume of steam; but the velocity with which the 
water issues from the nozzle, even with a head of 100 feet, is only 
about 80 feet per second. The water possesses kinetic energy 
largely because of its weight. With steam, this is very different, 
for a cubic foot of steam at a pressure of 100 pounds per square inch, 
gauge, weighs only about 34 pound, as compared with 6234 pounds for 
a cubic foot of water; that is, the water is 250 times as heavy as the 
steam. But when steam at 100 pounds pressure is allowed to ex¬ 
pand in a nozzle so that it comes out at atmospheric pressure, the 
jet of steam leaving the nozzle will have a velocity of 2500 feet per 
second. So, while the steam weighs only 1-250 as much per cubic 
foot, its velocity is 31 times as great as in the case of the water, and 


6 


so its kinetic energy is - -4 times as great as that of an equal 

quantity of water. 

This style of turbine is known as an impulse turbine, because its 
motion depends on the impulse, or striking of the steam against the 
curved buckets. Now, it has been found that for wheels of the 
impulse type, the greatest efficiency of operation is obtained when 
the buckets move just half as fast as the steam that comes from the 
nozzle. Thus, with a steam velocity of 2500 feet per second, the 
rim of the turbine wheel would need to moveata speed of 1250 feet per 
second, corresponding to 75,000 feet per minute, or almost 15 miles 
per minute. This speed is too high for safety, except for small wheels, 
and so the rim speed is not allowed to go beyond about 1400 feet 
per second, and even then the rotative speed is exceedingly high. 
For instance, the De Laval 300-horsepower turbine is almost 30 
inches in diameter and makes 10,600 revolutions per minute, with a 
vane speed of 1384 feet per second. The result is that this type of 
turbine cannot be directly connected to the machinery it is to drive 
because its speed is too great. Accordingly, a reduction of speed is 
obtained by suitable gearing. 



T-3 


The curves shown here indicate the change due to the free 
adiabatic expansion of 1 pound of dry saturated steam from 180 
pounds absolute (165 pounds gauge) to 1 pound absolute, or 1 
pound above vacuum. Adiabatic expansion means expansion of the 

7 














































steam without adding any heat to it or taking any heat away from it; 
that is, it is the sort of expansion that would occur in a nozzle made 
of a substance that would not let heat pass through it in either 
direction. Under such conditions, the work done by the steam in 
expanding is all used in giving velocity to the steam. 

The scale at the left indicates pressures, the vacuum line being 
marked zero. Distances in a horizontal direction represent values 
according to the scales marked along the curves. The curves of 
volume and velocity are of particular importance. Starting from 
the top horizontal line, representing 180pounds, the velocity increases 
fairly rapidly, while the volume increases slowly; but below the 100- 
pound pressure line the volume increases much more rapidly than 
the velocity. Now, these curves are based on a discharge of 1 
pound of steam per second, or a constant weight discharged. The 
area of the nozzle at any point, therefore, must be equal to the 
volume divided by the velocity, both taken at the same point or at 
the same pressure line on the curve. 

Assuming a nozzle whose cross-section is circular, the diameters 
at various points along the nozzle are indicated by the curve at the 
extreme left. Notice that this curve, on leaving the 180-pound pres¬ 
sureline, moves to the left rapidly, falling slowly, showing that the 
diameter of the nozzle decreases during the early stages of ex¬ 
pansion. Then the curve becomes almost vertical, for a long dis¬ 
tance, showing that the diameter does not change much. But 
below the heavy horizontal line draw across the diagram at the 
point corresponding to 108 pounds, the curve slants a little to the 
right, showing that the diameter of the nozzle increases slightly 
while the steam expands from 108 pounds. The point where the 
diameter is smallest is where the curve comes closest to the left edge 
of the diagram, corresponding to the heavy line at 108 pounds, 
which is6-10 the initial pressure, since 180 X 6-10 = 108. In other 
words, if steam is expanded completely in a nozzle, the nozzle must first 
converge, or grow narrower, and then diverge, or grow larger, and 
the point where it is smallest, known as the throat , will be at the 
point where the pressure is 6-10 of the initial absolute pressure. 

The nozzle used in the De Laval turbine shown in view T—2 was 
of this kind. At first, it decreased rapidly in area until the throat 
section was reached, after which it gradually increased in area. 
The converging part is usually very short as compared with the 
diverging part. The diverging part is made long enough to dis¬ 
charge the steam in lines parallel to the center line of the nozzle. 


8 



In connection with the single-stage De Laval turbine previously 
shown, it was pointed out that one of the difficulties met with by 
allowing the entire expansion of the steam to occur at one time was 
the exceedingly high velocity produced. This objection can be 
overcome, however, by dividing up the expansion so that it occurs in 
a large number of nozzles in succession. By doing this, the velocity 
developed by each expansion is much less than when the complete 
expansion takes place in one nozzle. When the expansion occurs 
in a large number of nozzles, one after the other, the turbine is called 
a multi-stage turbine. 

A De Laval multi-stage turbine of the impulse type is shown in 
this view. It is simply a number of single-stage turbine wheels 
keyed to the same shaft, and each separated from the others by 
partitions, so that each wheel turns in a chamber,'or cell, by itself. 
The high-pressure steam enters the turbine through the passage of 
semicircular cross-section at the middle of the picture. This 
passage extends all the way around the shaft, and from it lead the 
nozzles in which the first stage of the expansion occurs. There are 
only a few nozzles in the first partition, and they are spaced equally 
around the wheel. 

The high-pressure steam flows through the first set of nozzles, 
and expands somewhat in doing so. This expansion gives the steam 
increased velocity, so that it is moving rapidly when it leaves the 
nozzles. On leaving the nozzles, it strikes the blades on the edge 
of the first turbine wheel, turns this wheel (and consequently the 
whole rotor) and emerges on the other side of the first wheel. By 


9 




































this time its velocity is greatly reduced, because the steam gives up 
much of its energy of motion of the first wheel. 

From the first wheel chamber the steam passes into the nozzles 
in the second partition, where it expands further and has its pres¬ 
sure lowered by the expansion, but has its velocity increased again 
by the change of heat energy to kinetic energy. On emerging from 
the second set of nozzles, the steam strikes the vanes on the second 
wheel and gives up much of its energy to them, thus aiding in turn¬ 
ing the rotor. The steam leaves these vanes with its velocity 
greatly lessened, and passes into the nozzle in the third partition. 

In the third set of nozzles another stage of expansion occurs, and 
again the velocity of the steam is increased, so as to enable it to do 
further work on the vanes of the third wheel, and this same series of 
operations is repeated throughout the whole series of wheels. By 
the time the s.team reaches the left-hand end of the turbine, its pres¬ 
sure is low, because each expansion lowers the pressure somewhat. 
From this low-pressure end the steam is led away to the condenser. 

There are several interesting points to be observed in connection 
with this slide. In the first place, note that each turbine wheel 
has holes through it about midway between the vanes and the shaft. 
This is done to lighten the wheel. There is no danger that steam 
will escape from one side of the wheel to the other through 
these holes, because the pressure on opposite sides of the same wheel 
is the same; in other words, each wheel rotates in a cell filled with 
steam of a uniform pressure. The velocity decreases in passing 
through the moving vanes and increases during expansion in the 
nozzles, but the pressure changes only during expansion, when it 
decreases. 

Another feature to be noted is the increase in the length of the 
vanes towards the low-pressure end of the turbine. The reason for 
this is easily explained. When steam expands, its volume increases, 
in order to make room for the increased volume of steam after each 
expansion, the blades or vanes are gradually lengthened, so that the 
steam finds a gradually increasing space to accommodate its growing 
volume. 

The number of nozzles is likewise increased toward the low-pres¬ 
sure end; that is, where only a few nozzles are used in the first 
partition, the number is considerably larger in the last partition, so 
that the steam acts on a greater part of the circumference of the last 
wheel than on the first wheel. 

The nozzles in which the expansion takes place are not of the 


10 


type shown in the single-stage De Laval turbine; that is, they do not 
converge to a throat and then diverge toward the outlet end. For 
where the expansion is divided into such a large number of stages, the 
drop of pressure at each stage is small, and consequently the outlet 
pressure of each nozzle is considerably greater than 6-10 of the inlet 
pressure. When this is the case, there is no advantage to be gained 
by making a nozzle with a throat. It may be made a straight 
parallel hole, or it may even be made converging, or tapering toward 
the outlet end. 

To prevent too high a rotative speed, the turbine is provided with a 
governor, indicated by the cylinder at the top of the vertical spindle 
at the right-hand side of the view. This governor is of the centri¬ 
fugal type and receives motion from the main shaft of the turbine 
through a worm and worm-gear drive. When the speed rises above 
the normal, the governor weights are moved outward by the in¬ 
creased centrifugal force and this movement is transferred to a 
throttling valve in the steam-supply pipe, closing this valve some¬ 
what, thus throttling the steam and-so reducing its pressure. This 
reduction of pressure lessens the work done and so reduces the speed 
to the normal. There is an emergency governor, also, which acts 
only when the speed gets beyond the control of the ordinary governor 
and when the emergency governor acts, the steam supply is cut off 
and the turbine is stopped. 

Since the partitions between the cells are stationary, it is evident 
that the rotor shaft must turn in the holes through the centers of the 
partitions. To prevent the steam from leaking from one cell to the 
next, along the shaft, some means must be used to obtain a tight 
joint at these points, without causing too much friction. Similarly, 
it is necessary to provide against leakage where the shaft passes out 
through the ends of the casing around the rotor. The methods of 
accomplishing these objects are shown by the next two slides. 


11 



This slide shows how leakage between the rotor and the partitions 
is prevented. Each wheel is made with a long hub that projects to 
one side, and this hub is pressed on over a tapered sleeve that is 
slipped over the shaft. The wheels are prevented from turning 
around on the shaft by keys that enter the shaft and the hubs. 
The outside diameter of the projecting hub is but slightly less than 
the diameter of the circular opening in the partition. Along the 
inside of this opening are inserted five packing rings, shown by the 
short black lines, and the inner edges of these packing rings bear 
against the outer face of the wheel hub. For the steam to pass from 
one cell to the next, therefore, it must leak through five successive 
joints between these rings and the hub. The spaces between the 
packing rings collect moisture, and this moisture aids in sealing the 
joints and preventing leakage. Such a package as this, which causes 
the steam to travel in a winding path in order to get by, is called a 
labyrinth packing. There is not a great deal of difference between 
the pressure on opposite sides of a partition, and so leakage is not 
so difficult to prevent as when the pressure difference is great. 


12 








































The form of labyrinth packing used where the rotor shaft passes 
through the casing is shown here, A thin sleeve is slipped over the 
shaft, and against this sleeve press four carbon packing rings, each 
of which is free to move laterally in the cast iron box containing 
the rings. Thus, if the shaft has a slight sidewise movement due to 
lack of balance of the rotor at high speeds, the rings remain in con¬ 
tact with the sleeve, but move in relation to the box. The rings 
are sectional, or made in a number of segments,which are held to¬ 
gether around the shaft by coiled wire springs. 


13 
















T-7 


Here is shown the wheel of a Westinghouse impulse turbine, 
together with an expansion nozzle and a set of reversing vanes. The 
wheel is a disk of steel plate and is bolted to a hub that is rigidly 
fastened to the shaft. The expansion nozzle and the reversing 
vanes on the opposite side of the wheel are stationary, since both are 
bolted to the casing of the turbine, and the wheel rotates between 
them. On leaving the nozzle at high velocity, the steam strikes the 
vanes on the wheel, passes through them, and after imparting 
motion to the wheel emerges on the opposite side. But in passing 
through the wheel vanes its direction is almost completely reversed; 
that is, it is turned back on itself. When it escapes on the other side 
of the wheel, it is caught in the wide, curved reversing vanes, and in 
following the passages between these its direction is again changed 
so that it is again directed against the wheel vanes, on the opposite 
side of the wheel, but at the same angle as when it left the nozzle. 
Thus, the steam is made to exert its force on the wheel vanes twice 
during its passage. After striking the wheel vanes the second 
time, the steam comes out on the same side as the nozzle, and is 
then led away to the condenser. 

By having the steam pass twice through the wheel in order to 
give up its kinetic energy, the turbine has two velocity stages, al- 


14 




though it has but one set of moving vanes. This type is also some¬ 
times called a reentry turbine, because the steam reenters the wheel 
after its first action. This principle is used in a number of small 
turbines by various manufacturers and is often termed the Riedler- 
Stumpf principle,because it was first practically developed by the 
two German professors, Riedler and Stumpf. 



T-8 

The Westihghouse two-stage impulse turbine operates on the 
same principle as the one just shown, but there are two nozzles and 
two sets of reversing vanes in series. The expansion of the steam 
from the boiler pressure to the exhaust pressure occurs in the two 
nozzles, and as the drop of pressure in each is considerably more 
than 60 per cent., the nozzles are of the type having a throat and a 
diverging section. The reversing chambers simply change the 
direction of the steam and send it through the wheel again. As 
the steam has increased volume after it first expansion, the second 
nozzle and the second set of reversing passages are considerably 
larger than the first. 


15 












T-9 

This is the Sturtevant single-stage impulse turbine, with one 
half of the casing unbolted and set aside so as to show the wheel 
and the inside arrangement. In this turbine, the vanes or buckets 
are cut in the outer circumference of the wheel, and the steam 
from the nozzles, instead of being injected from the side, at an 
angle, enters opposite the edge of the wheel, something after the 
fashion of the water in the buckets of the Pelton water wheel 
shown in the first slide of this lecture. 

Any desired number of nozzles may be used, set at equal dis¬ 
tances around the rim of the wheel. In the turbine shown, there 
are ten, and these are carried by the half of the casing that is re¬ 
moved and that is shown at the right. The nozzles are of Tobin 
bronze and each is cast in one piece with a set of reversing vanes, 
forming three or four reversing chambers. When the casing is 
bolted in place, these reversing vanes almost completely surround 
the outer edge of the wheel. 

The complete expansion of the steam takes place in each nozzle, 
and the steam at high velocity enters the buckets, is thrown back 
out of them into the first reversing chamber, then back into the 
wheel buckets again, out into the second reversing chamber, back 
into the wheel a third time, out into the third reversing chamber, 
and so on, being finally exhausted from the turbine casing. Thus, 
it is of the Riedler-Stumpf type. It is governed by a throttling 
governor and has an emergency governor for operating in case of 
unsafe speeds. 


16 





T-10 

This slide shows the construction of the Terry turbine. The 
wheel is built up of two flat circular plates held together by bolts 
through the hub and near the rim. The vanes or buckets are steel 
punchings fitted into grooves in the disks, between which they are 
held. There are several nozzles carried by the casing of the turbine 
and set in the plane of the wheel. In addition, each nozzle has 
several reversing vanes, similar to those just shown. Thus, the 
Terry turbine is of the reentry type also, and in its action is very 
much like the Sturtevant. 

The steam enters the turbine through the flanged fitting at the 
left-hand side, beneath the shaft. At this point there is a throttling 
valve, the stem of which is under control of the governor, which is 
inside the opened casing at the end of the shaft. Thus, the speed 
of the turbine is regulated by throttling the steam supply. The 
steam leaves the turbine through the exhaust connection at the 
bottom. 


17 





T-l 1 

This is another view of the Terry turbine, the upper part of the 
casing being broken away to show the location of the nozzle and re¬ 
versing vanes with respect to the wheel. The expansion is com¬ 
pleted in the nozzle, so this turbine belongs to the single-stage ex¬ 
pansion class. The valve at the left enables the flow of steam into 
the nozzle to be stopped, in case the number of active nozzles is to be 
reduced. 


18 








T-12 

One of the most common uses of the steam turbine is for driving 
centrifugal pumps by direct connection. Here is shown a Terry 
turbine of 135 horsepower, running at 1300 revolutions per minute, 
directly connected to a centrifugal pump capable of delivering 2775 
gallons per minute to a height of 140 feet. Both are bolted to 
the same base plate and their shafts are connected by the flange 
coupling at the middle. The upper halves of the casings and the 
bearing caps are removed to show the construction clearly. 


19 





T-13 


Another type of impulse turbine is the Curtis, but this turbine is 
of the kind that has several pressure stages and several velocity 
stages as well, that is, there are several chambers, to each of which 
there corresponds an expansion of the steam and a change of velo¬ 
city, but the pressure of the steam does not change while it flows 
through one chamber. 

At the right in this view are shown sections of the nozzles and 
vanes for one stage of the Curtis turbine. The middle row of vanes 
is stationary, being fixed to the shell or casing of the turbine. The 
rows on both sides are fastened to the same wheel and so rotate at 
the same speed. The steam flows through the nozzles, expanding 
as it does so, and thus having its kinetic energy greatly increased. 
It strikes the first row of moving vanes, gives up energy to them and 
emerges on the other side in a reversed direction. Here it is caught 
by the stationary vanes and reversed again, so that it has the same 
direction of flows as on leaving the nozzles, after which it enters the 
second row of moving vanes and gives up more of its kinetic energy. 

From the time it leaves the nozzles until it leaves the second row of 
moving vanes, its pressure does not change, but the velocity de¬ 
creases in each row of moving vanes. To restore its velocity and 
enable it to do further work, it is led to another set of nozzles, where 
it expands again, with a further drop of pressure and then passes 
through another set of two moving vanes and one stationary set. The 


20 








number of such successive stages can be increased until the steam 
has been expanded down to the exhaust pressure. 

The shape of the vanes can be seen very clearly in this view. The 
edges are thin and sharp, so as not to check the flow of steam or 
cause eddies, and the middle is thick, to give the necessary strength 
and likewise to make the passages between the vanes of practically 
uniform width. For since the pressure does not change while the 
steam is passing through each set of three rows of vanes, the volume 
does not change, and so it is not necessary to provide wider passages 
at one point than another. 

At the left is shown a series of high-pressure nozzles, all formed in 
one casting. The view shows the outlet of vanes from the side, as in 
De Laval turbine, and the rows are on the outer edge of a circular 
wheel, the nozzle must be in the arc of a circle, which explains why 
the nozzle casting is of the shape shown. 



T-14 

In the Curtis turbine, the several stages are separated by dia¬ 
phragms or partitions, and in these partitions are placed the nozzles 
by which the steam is given its velocity for the succeeding stages. 
This slide shows a five-stage Curtis turbine with the upper half of 
the casing removed. The five wheels, each with two rows of vanes 
are plainly visible, but the stationary vanes cannot be seen because 
they are fastened to the casing, which has been removed. The 
wheels are separated by partitions, so that each wheel revolves, 


21 








in its own chamber, or cell. These partitions extend from the casing 
in to the shaft at the center, where they are fitted with packing 
rings that bear against the wheel hubs and prevent leakage from one 
cell to the next. Nozzles are formed in each partition, as can be 
seen in the side of the partition at the extreme right. 



T-15 

The shaft and rotor of a four-stage Curtis turbine are shown here. 
This view shows clearly that the outer ends of the vanes are riveted 
into a ring or band that extends all the way around the wheel, 
giving a rigid, strong construction. This band is called a shroud, 
and the vanes are said to be shrouded. 


22 









T-16 

A diaphragm or partition from the low-pressure end of a Curtis 
turbine is illustrated in this view. The openings around the outer 
edge are the entrances to the expansion nozzles and the opening at 
the center is the hole through which the shaft and wheel hubs pass, 
and into which the packing ring is bolted. 


23 





T-17 

The methods of fixing the vanes to the wheels of two different 
makes of turbines are shown here. At the left is a Curtis wheel with 
a single row of vanes, and the shape of one of the vanes is shown in 
the upper center of the slide. The vane has a head formed at its 
inner end,and theshape of this head corresponds to that of a dovetailed 
groove turned in the rim of the wheel. The heads of the vanes are 
inserted into the dovetailed groove at one point, and the vanes are 
then slid around the wheel to their places, with blocks inserted be¬ 
tween them to give the necessary spacing. 

The outer end of each vane has a short tongue formed on it, 
and when all the vanes are in place a shroud band is drawn around the 
wheel. This band has openings in it, through which the tongues on 
the vanes project, and these tongues are riveted over, thus holding 
the shroud band firmly and stiffening the entire row. The inner 
ends of the vanes are likewise calked into the groove in the wheel, 
so that both ends are held securely. 

The vane shown at the bottom in the center of the slide is of the 
kind used in the Parsons turbine ard the view at the right shows 
how such vanes are arranged and held. These will be further re¬ 
ferred to later. Many engineers refer to the vanes by the term 
blades. The three names—blades, vanes and buckets—are used 
indiscriminately. 


24 






t««n« l«nri am hmtim 


T-18 

The shape and arrangement of the vanes or blades of three 
different turbines are shown by these diagrams. At the bottom is 
the Curtis, which was explained before. It consists of a set of 
expansion nozzles and two rows of moving vanes separated by a 
stationary row that changes the direction of flow of the steam. 

At the middle is the Rateau turbine arrangement. In this 
turbine, there are a large number of wheels, each fitted with one 
row of vanes, and each rotates in a cell separated from the others by 
partitions. The steam enters each wheel from a set of expansion 
nozzles by which velocity and kinetic energy are given to the steam. 
Thus, the Rateau arrangement consists of alternate rows of nozzles 
and movable vanes. Each set of nozzles and the vanes next to it, 
taken together, constitute one stage, and in each stage the pressure 
is lower than in the preceeding one. The Rateau nozzles have 
parallel sides at the outlet end; that is, they do not diverge, be¬ 
cause the drop in pressure during expansion is not so great that the 
outlet pressure is less than 60 per cent of the inlet pressure. 

At the top is shown the arrangement of blades in the Parsons 
turbine. These consist of alternate rows of stationary and moving 
blades, the first row at the left being stationary, the next a moving 
row, the third stationary, and so on. The principle of the Parsons 
turbine will be explained in later views. 

The action of ihe steam in the Parsons steam turbine is different 


25 


























from the action in impulse turbines of the types that have thus far been 
considered. The impulse turbine receives its turning forces from 
the velocity of expanded steam discharged from nozzles, and the 
whole expansion takes place in the nozzle, there being no expansion 
of the steam while passing through the moving vanes. In the re¬ 
action turbine, however, the expansion is continuous; that is, the 
steam in passing through the stationary and moving vanes is con¬ 
stantly losing pressure and increasing in volume. This is the chief 
feature marking the difference between the two types. 





This slide will serve to illustrate how the reaction type of turbine 
acts. Four rows of Parsons blades are shown here, marked A. B. C. 
and D. Of these, A and C are guide vanes which change the di¬ 
rection of the steam, and are stationary, while B and D are movable 
rows. The steam entering the Parsons turbine first of all meets the 
first row of guide vanes, enters the spaces between them, and flows 
through. Since the total drop of pressure from the inlet to the ex¬ 
haust is divided among many sets of blades, the drop through each 
set is small, and hence the expansion of the steam in one row is not 
great. 

The first row of guide blades, therefore, serves a double purpose. 
It gives the steam the proper direction so as to strike the first row 
of moving blades at the proper angle; and it also acts as a series of 
nozzles in which expansion occurs, to give the steam velocity. But 
as the expansion is small, the openings between the blades are of the 
converging type. When the steam escapes from the row of guide 
vanes, therefore, and enters the first row of moving vanes, it has 
both velocity and pressure. 


26 






















When the steam strikes the movable vanes, it gives up to them 
some of the kinetic energy due to its velocity, and this turns the 
wheel to which the vanes are attached. But in passing through the 
passages between the moving vanes, the steam changes direction 
and continues to expand, just as it did in the first guide vanes. 
The expansion is accompanied by an increase of velocity; but in 
acting to cause this increase of velocity, an equal force reacts against 
the vanes, and this reacting force adds to the pressure that turns the 
wheel and rotates the turbine. It can now be understood why this 
type of turbine is called a reaction turbine. 

The reaction idea can be very simply explained. If you stand in a 
boat and push against a dock, the boat will move away from the 
dock, and the harder you push, the more rapidly will the boat move. 
For the same pressure you exert with your hands against the dock is 
exerted by your feet against the boat in the opposite direction. 
This is what is meant by saying that action and reaction are equal 
and opposite in direction. 

Now, in the case of the steam expanding in the moving vanes, the 
same thing occurs. The increased velocity of the steam is due to a 
force that, as it were, gets behind it and pushes it along faster; but 
this force that pushes the steam along has to brace itself against 
something, so to speak, and the thing it braces itself against is the 
row of moving vanes. The result is that it reacts, or “kicks back” 
against the blades, just as hard as it pushes the steam forward. 

Although the two types of turbines are thus distinguished, be¬ 
cause of the principal features of their action, the truth of this 
matter is that each acts partly on the principle of the other. That 
is, every impulse turbine has a certain amount of reaction effect 
in it, and every reaction turbine has some impulse effect. Never¬ 
theless, this method of division is simple and is widely adopted. 
Hence, if there is no change of steam pressure in the moving vanes, 
the turbine is considered as being of the impulse type, and if the 
pressure falls and expansion occurs in the moving vanes, the tur¬ 
bine is considered as being of the reaction type. 


27 



T-20 


A longitudinal section of the Westinghouse-Parsons turbine is 
shown in this view. The rotor is horizontal and is supported by a 
shaft that is held in suitable bearings at the ends. The rotor is not 
of uniform diameter throughout, but is divided into sections having 
different diameters. Starting at the right-hand end, where the 
shaded part of the rotor begins, and proceeding toward the left, it 
will be observed that there are three sections of practically the 
same diameter. The only difference between these is that the rows 
of blades in the second section are farther apart than in the first 
section, and those in the third section farther apart than those in the 
second. Also, as can be seen by the shading at the outer edges of 
these sections, the blade lengths increase from the first to the third 
section. The reason for this is that the steam expands on its way 
through the successive rows of vanes, and there must be increased 
space to accommodate it; so the blades are set farther apart and made 
longer in the second and third sections. In any one section however 
they are all of the same length and equally spaced. 

After the steam has passed the third section, and reached about 
the middle of the rotor, it is no longer practicable to provide in¬ 
creased space by changing the length and spacing of the blades; 
so the diameter of the rotor is increased and the blades are set 
closer together again in the first part of this large section. In the 
remainder of it the length and spacing of the blades are increased. 

By this time the steam has reached a low pressure and its volume 
is great; so the diameter of the rotor is again increased, and in this 


28 















largest section the lengths oi the vanes are increased rapidly toward 
the low-pressure end. 

The moving vanes are all attached to the rotor; but the station- 
aiy vanes, or guide vanes, are fastened to the steam-tight casing 
surrounding the rotor and are in rows that alternate with the rows 
on the rotor. The steam, enters the first row of guide vanes at the 
small end of the rotor, flows through into the first row of moving 
vanes, then on into the second row of guide vanes, and so on in the 
same way to the large end of the rotor, where it is discharged into 
the passage leading to the exhaust. 

The governor, which is driven from the shaft and is shown above 
the right-hand end of the shaft, controls the speed of the turbine by 
regulating the amount of steam admitted. It does not throttle the 
steam, because that would lower the pressure of the steam. In¬ 
stead, it always admils steam at full pressure, but it controls the 
action of the inlet valve so that it is open for a greater or shorter 
time, thus regulating the speed. This will be explained later in 
connection with another slide. 

The main inlet valve is directly above the high pressure end of 
the rotor and is of the double-seated poppet type. Under normal 
conditions of load, all the steam flows through the whole length of 
the rotor. But in case of a temporary overload, the other poppet 
valve is opened, thus admitting high-pressure steam into the low 
pressure stages of the turbine and so increasing the power developed. 
When this is done, however, the steam is not used to the best ad¬ 
vantage, and the economy of the turbine is lowered. 

With such a heavy rotor, on such a long shaft, it is very necessary 
to have extremely accurate baUncing; otherwise, at the high speeds 
of rotation, there would be excessive vibration. Pei feet balancing 
is next to impossible; so, to prevent vibration, the shaft is made 
large and stiff, but the bearings are made flexible. This is accom¬ 
plished by making each bearing consist of several sleeves, one 
fitting loosely over the other. The sleeves are prevented from turn¬ 
ing by dowel pins, and oil is pumped into the bearing under a slight 
pressure. This oil flows between the sleeves where it forms thin 
films of yielding oil, so that, when there is any vibration of the shaft 
due to unbalance, it is all taken up by these sleeves and oil films, 
and is not communicated to the frame of the turbine. The amount 
of movement of the ends of the shaft in these bearings is, of course, 
extremely small; yet it is enough to overcome the vibration evil. 

In flowing through the vanes, parallel to the axis of the rotor, 


29 


the steam exerts an endwise pressure, and if no means were adopted 
to counteract this pressure, there would be a heavy axial thrust on 
the shaft. By means of three balance pistons P, as they are called, 
this thrust is overcome. As may be seen, these three pistons are 
fixed to the rotor shaft at the right-hand end, and they have the 
same diameters as the three main divisions of the rotor. The high- 
pressure steam, entering the rotor at A, therefore, presses to the left 
against the rotor and to the right against the exposed part of the 
smallest balance piston. As the diameters are equal and the areas 
exposed to pressure are the same, the two forces neutralize each 
other. By means of pipes E, the remaining rotor sections and bal¬ 
ance pistons are put in communication , so that the same steam 
pressure acts on them in opposite directions, and so prevents end 
thrust. 

Practically, however, it is not possible to eliminate all end thrust 
by this means, although it can be reduced to a small amount. To 
take care of any unbalanced pressure endwise of the shaft, a thrust 
bearing is formed on the shaft between the right-hand bearing and 
the extreme right-hand end. This bearing consists of a series of 
collars that fit into corresponding grooves in a box held in the frame 
of the turbine. This box can be moved endwise by means of two 
adjusting screws, one above and one below, acting through short 
levers pivoted to the frame. Thus, in addition to serving as a 
thrust bearing, the box enables the rotor to be adjusted slightly 
in an endwise direction, thus regulating the clearance between 
adjacent rows of vanes. 

In running reciprocating engines, engineers are able to keep 
the machinery" going when a bearing begins to heat, by nursing it 
and watching it carefully, but this is out of the question in turbine 
work. The shaft speeds are so high in turbines, as compared with 
engines, that if a bearing begins to heat, the trouble gets worse so 
rapidly that the ordinary remedies fail. Therefore, it is cf the first 
importance to see that the lubricating system of the turbine is in 
proper working order. To prevent unexpected failure of the oiling 
system through clogging of oil pipes or holes, all the oil should be 
carefully strained through a fine wire-mesh strainer. 

The pressure oiling system is used on most of the large steam tur¬ 
bines, the oil being pumped under pressure to the various bearings, 
from which it drains back to the inlet side of the pump, where it is 
drawn through a strainer and forced back to the bearings. The 
pump is driven from the rotor shaft. 


30 



T-21 

The appearance of the rotor of a Westinghouse-Parsons turbine, 
removed from the casing may be seen here. These views also show 
the position and construction of the balance pistons clearly. The 
upper one is from a 1000 kilowatt generating unit designed for 3600 
revolutions per minute. The lower one is for the same power of 
turbine running at only 1500 revolutions per minute. 


31 





T-22 


The blades or vanes of a Westinghouse-Parsons turbine are shown 
by this slide. The rotor has grooves cut in it, into which the ends 
of the blades are set. The proper spacing is secured by distance 
pieces that are located between the blades in the grooves. The 
outer ends of the blades are held by a ring of wire that is threaded 
through holes in the blades. If the blades are more than 6 inches 
long, more than one ring of wire may be used. The blades on the 
low-pressure end of the large marine turbines of this type may be 22 
inches long. 

The hole through which the wire is threaded is shaped like a comma 
(,); that is, it is circular, with a nick at one side The wire has 
exactly the same shape of cross-section. After the wire has been 
put through all the holes in a row, the part of the wire between each 
two blades is given a quarter twist which locks it in place and 
prevents the outer ends of the blade from moving either close to¬ 
gether or farther apart. The spacing block fits down over the lug 
formed on the inner end and thus prevents the vane from flying out 
of the groove. 

One of the troubles that is likely to be met with in operating a 
steam turbine is the stripping or breaking of the vanes, such as would 
happen if the moving vanes should rub against the stationary 
vanes, nozzles, partitions, or casing. Before this could happen, the 
rotor would have to shift out of its proper position. Such move¬ 
ment of the rotor might be caused by faulty adjustment of the 
thrust bearing cr the main bearings. 


32 






Another thing that might cause interference of the blades is 
unequal expansion. In starting a cold turbine, the warming-up 
process should be carried out slowly and carefully, because, if steam 
is turned on too rapidly, some parts of the turbine will be heated 
more quickly than others, which will cause unequal expansion; and 
as the clearance between the moving and stationary blades is slight, 
this unequal expansion may bring the vanes into contract and either 
break them or tear them off. 

If any solid matter should be carried into the turbine by the 
current of live steam, the chances are that seme of the blades would 
be damaged: therefore, it has been found advisable to install 
strainers on the inlet pipes in order to catch all foreign matter that 
might cause trouble. Stripping of the blades is apt to happen only 
in those turbins which have the vanes inserted into slots or grooves 
in the rotor wheel. If the buckets are machined in the body of the 
wheel itself, they may be damaged by rubbing or dented by in¬ 
terference, but they are not likely to be stripped. 

Another operating trouble to which steam turbines are subjected 
is the wearing away of the edges and faces of the vanes duetothe cut¬ 
ting action of the steam in passing through them. As has been pointed 
out, the steam has very high velocities and frequently carries mois¬ 
ture with it. The effect of the steam and the moisture rubbing- 
over the vanes at such high speed is to wear away the sharp edges of 
the vanes, and the curved surfaces. This is called erosion. 

Of course, the amount of erosion will depend on the material of 
which the vanes are made, the processes by which they are manu¬ 
factured, and the amount of moisture in the steam. What is true 
of the vanes is also true of the expansion nozzles, as they are subject 
to erosion also. As nearly as can be determined from the results of 
experience, perfectly dry saturated steam and superheated steam 
have little or no effect on the vanes so far as erosion is concerned. 
But as the steam grows wetter the wear glows greater, and it also 
increases as the velocity of the steam increases. One of the ad¬ 
vantages of the turbine, however, is that an ordinary amount of 
erosion of the vanes does not seem to cause any great loss of power 
or efficiency. For example, in the case of a single-stage De Laval 
turbine of 100 horsepower, the edges of the vanes on the nozzle or 
inlet side were worn away 1-16 inch, yet the steam consumption was 
only 5 per cent above what it was when the vanes were new. 


33 


T-23 


The method of governing the Westinghouse-Parsons turbine may 
be studied in this view. The right-hand valve, which admits steam 
to the rotor, has a vertical stem, at the upper end of which is a 
heavy coiled spring against which the valve must open. About the 
middle of the valve stem is fixed a piston that works in a short cylin¬ 
der as the valve stem rises or falls. From the lower end of this 
cylinder a port leads off to the left to a short vertical pilot valve, 
as it is called, that works up and down in a steam chest to which 
high-pressure steam is supplied. 

The pilot valve is given its continuous up-and-down motion by an 
eccentric driven from the rotor shaft through gearing. As a result 
of its motion, the port leading to the space beneath the piston on the 
admission-valve stem is opened and closed, so that steam is alter¬ 
nately admitted and exhausted from beneath that piston. As a 
consequence, the admission valve is given an up-and-down move¬ 
ment, which admits puffs of steam at full boiler pressure into the 
turbine. The length of these puffs depends on how long the ad¬ 
mission valve is held open, and that is controlled by the governor. 

The lever by which the pilot valve is moved is pivoted on a pin 
whose position is varied by the governor. The effect of changing 
the position of this pivot is to change the length of time that the 
pilot valve admits steam to the space under the piston on the ad¬ 
mission-valve stem, which in turn governs the length of time that 
valve stays open. Thus, if the speed of the turbine rises, the gover- 


34 

































nor is affected and shifts the position of the pivot point of the pilot- 
valve lever. This causes the pilot valve to admit steam under the 
piston for a shorter period; and as the main admission valve is 
thus held open for a shorter time, the puffs of steam are of shorter 
duration, and so the steam supply is reduced without reducing the 
pressure. This results in bringing the speed back to normal. If 
the speed gets too low, the admission valve is acted on to admit 
longer puffs—but still the same number as before—so as the speed is 
increased. 

The left-hand valve is practically a duplicate of the right-hand 
valve, and has a pilot valve, also, by which it is operated in the same 
way; but this second valve does not come into action until the load 
becomes excessive. When the load rises beyond a certain value, the 
pilot valve on the left-hand admission valve is brought into action 
and high-pressure steam is admitted directly into the low-pressure 
stages of the turbine. This is not efficient, but it enables the tur¬ 
bine to meet sudden heavy overloads. The lever at the top of the 
right-hand admissicn-valve stem can be used to hold this valve open 
by hand while starting the turbine or warming up preparatory to 
starting. 



COVER 


TRIGGER CAM BUSHJNG(uuT£JCf) 

TRIGGER CAM SHAFT - 
trigger CAM bushing (wsolc 
. TRIGGER CAM-W 
vEIGHT SPRING RETAINER LOCK ^ ^ 


VALVE LEVER 
.VALVE LEVER PIN 
.VALVE LEVER PLATE 


-TRIGGER PLATE 
—TRIGGER STOP 
--TRIGGER 


-VALVE BODY COVER 
-VALVE BODY (UPPER) 

-VALVE SPRING ADJUSTING SCREW 
-VALVE SPRING RETAINER (UPPER) 
-VALVE SPRING 

-VALVE SPRING RETA1NER(10W;r) 
-VALVE BOW .(LOWER) 


BALANCING BLOCK ' 

BALANCING 

... ' ’ weight s mm/ 

wgffcHT SPRING RETAINER W 
BODY LOCKING SCREWS 
Wight spring retainer lock spring'' 


-VALVE 


T-24 


Every turbine should have an emergency stop that will act to 
stop the turbine in case the speed gets beyond control of the governor. 
The common way of arranging this device is to have a weight, 
acted on by the centrifugal force due to rotation, fly out and trip 
a mechanism when the speed gets dangerously high. The mechanism 


35 




thus tripped can be made to close the steam admission valve or some 
other valve in the steam-supply pipe, 

This slide shows the safety stop on the Westinghouse-Parsons 
turbine. It is at the high-pressure end of the rotor shaft and con¬ 
sists of a weight held in position by a spring. If the speed grows too 
great, centrifugal force throws this weight outward, overcoming the 
resistance of the spring, and the weight strikes the trigger cam. 
This action throws back the trigger and allows a spring to open a 
small valve that controls the admission of steam to a cylinder on 
the emergency throttle valve. The result is that steam is admitted 
and the throttle valve closed before the speed can rise much higher. 



T-25 


The saving due to carrying a high vacuum is more noticeable in 
the case of a steam turbine than with a reciprocating engine. If 
an exceedingly high vacuum is carried with a reciprocating engine, 
the temperature of the exhaust steam will be low, and the cylinder 
walls at exhaust will follow the drop of temperature of the steam. 
When steam is admitted on the next stroke, therefore, the loss due 
to initial condensation will be greater, because of the increased 
difference of temperature. 

Again, the high vacuum in the condenser of a turbine increases 
the number of expansions of the steam at the lower end of its range, 
and thereby utilizes heat that would otherwise be thrown away. 
The amount of extra heat converted, into work by increasing the 
vacuum from 28 to 29 inches amounts to a large percentage of the 
total heat converted into work. Hence, it is advantageous to carry 
a high vacuum on a condensing turbine. 


36 




































This slide shows a Leblanc condenser connected to a Westing- 
house turbine. The shaded parts are the parts that are under 
vacuum. A corrugated expansion joint is used between the tur¬ 
bine and the condenser to provide for expansion and contraction. 

In general, a steam turbine is started under much the same con¬ 
ditions as an engine. After making sure that the oiling system or 
oiling devices are in working order, the turbine is warmed up slowly. 
The steam for this operation may be admitted by opening the 
stop valve slightly, but a by-pass around the throttle is preferable. 
All drains from the turbine are kept open while the warming-up 
process is going on, in order to remove the condensation. When all 
parts have been brought to their working temperature, the drain 
valves are closed, and the rotor brought up to speed. 

If the turbine exhausts into an independent condenser, the air 
pump and circulating pump are started before the turbine is 
started. The load should be thrown on gradually. 

In stopping, the emergency stop-valve may be tripped. This 
will shut off high-pressure steam and the load will quickly bring 
the rotor to a standstill. Then all drain valves should be opened 
the condenser shut down and the oil feed cut off. 



T-26 

This view is from an actual photograph of a Westinghouse 
double-flow turbine with the upper half of the casing laid back to 
show the interior arrangement. The stationary blades are fastened 
to the casing, and it may be seen very plainly that the arrangement 


37 




and length of blades are the same in both directions from the 
middle. The reason is that in this turbine the steam enters the 
high-pressure stages at the middle, and flows towards the ends, thus 
giving the name “double flow.” At the middle of the rotor is a 
single-stage impulse wheel, against the vanes of which the steam is 
first directed from a number of expansion nozzles. This impulse 
wheel absorbs the kinetic energy of the steam, after which the steam 
divides, half of it flowing through the blades of the reaction turbine 
at each side of the middle. The exhaust steam leaves the casing 
at the ends and is led away to the condenser. 

Since the steam flows in opposite directions from the middle, the 
pressure in one direction is opposed by an equal pressure, in the 
other direction, and so it is unnecessary to use balance pistons or 
dummies, as they are often called. In large turbines of this type, 
the stationary blades are not fastened into grooves in the casing, but 
are held in a separate liner that is secured inside the shell. By this 
means the strains due to change of temperature are not likely to 
cause trouble. 

The steam valves at the front are operated by oil supplied under 
pressure. The governor controls them through pilot valves and 
floating levers, as previously described. On the shaft at the right 
of the turbine, at the lower end of the slanting pipe, is a water brake 
by means of which the power developed by the turbine can be de¬ 
termined. 



T-27 

A longitudinal section of a double-flow Westinghouse turbine is 
shown by this section. The only difference between this and the 
previous one is that this one has two impulse wheels at the middle. 
The steam enters at the bottom, at the middle of the casing, and from 
that point its course through the turbine can be followed by noting 
the arrows. 


38 



























T-28 


The most favorable combination for a steam turbine is a small 
diameter of rotor and a high speed of the vanes, because a maximum 
power will thus be obtained with a small weight of turbine and with 
high efficiency. But the result of this construction is a speed of the 
rotor, in revolutions per minute, too high for most work. Con¬ 
sequently, it is necessary to reduce the rotative speed of the shaft 
to which direct connection must be made. This reduction of speed 
is ordinarily accomplished by gearing, small gears being used on 
the turbine shaft and much larger ones on the driven shaft. 

This slide shows a Westinghouse-Parsons turbine driving a centri¬ 
fugal pump through reducing gears, which are contained inside the 
casing situated between the turbine and the pump. 


39 







T-29 

The style of gearing used in the reducing gear of a turbine is 
shown very clearly in this view. It consists of two large gears 
fastened to the driven shaft, meshing with two small gears fastened 
to the shaft that is directly connected to the rotor shaft. The 
speed ratio may be 10 to 1, so that, if the turbine makes 2500 
revolutions per minute, the driven shaft will make only 250 revolu¬ 
tions per minute. 

As will be noticed, the teeth on these gears are not parallel to the 
shafts on which the gears are fastened. Instead, they are at an 
angle, and the direction of slant of the teeth is opposite on the two 
gears. Such gearing is known aS spiral gearing, but if the two wheels 
on the same shaft are set very close together, or edge to edge, the 
gearing is known as herringbone gearing. 

The purpose of making the teeth slant is to reduce noise and 
vibration If ordinary spur gearing were used for such high speeds, 
the noise and vibration would be something terrific; but with the 
spiral teeth, there are parts of several teeth in action all the while, 
and so the clattering is prevented and smooth action is insured. 

But, with slanting teeth, an end thrust is set up, tending to push 
one shaft in one direction and the other shaft in the opposite direction. 
So, to neutralize this thrust, two such sets of gears are used, with the 
slant of the teeth opposed, so that the thrusts produced act against 
each other. With this construction, no thrust bearing is needed on 
either shaft. 


40 









T-30 

One of the problems in designing high-speed gearing of the type 
just described is to prevent unequal pressure on the teeth, because 
this would result in rapid wear. This slide shows the method used 
in the reducing gear of the Westinghouse marine turbine just shown. 
The shaft carrying the pinions, or small gears, is supported in three 
bearings, one between the pinions and one at each end. 

These three bearings are held in a framed, that has no rigid con¬ 
nection to the gear-box frame. The frame A is held between three 
pairs of pistons C, one pair of these pistons being located on opposite 
side of each of the three bearings. 

This view is a vertical section through one of the bearings, and 
shows the framed with the pistons C fitted into it above and below, 
the pistons bearing on the top and bottom E and F of the gear-box 
frame. There is a certain amount of clearance between the pistons 
and the bottoms of the recesses in A , as well as between A and the 
outside frames E and F. The clearance spaces under the pistons 
are filled with oil under pressure, the oil being supplied through 
passages that connect with the other pistons also. The result is 
that the long frame A simply floats on oil between the outside frames 
of the gear-box. 

When the pressure becomes excessive at one point, the frame A 
yields at that point by compressing the oil under the piston at that 
point. This relieves the pressure at that point, but at the same 
time forced the oil to some other point where the pressure was not so 


41 







great, thus equalizing the pressures on the gear teeth. Hence, this 
construction prevents excessive and unequal pressures on the gear 
teeth and likewise reduces the noise of operation. 



T-31 

This view shows a Curtis horizontal turbine direct connected to a 
500-kilowatt generator. The smaller Curtis turbines are generally 
governed by throttling the steam supply. In the larger sizes the 
governor sets in motion a form of valve that opens or closes the 
valves that control the supply of steam to the nozzles in the first 
stage of the turbine. These valves are not opened or closed to¬ 
gether, or at one time. Instead, they are opened one after the 
other, as the load increases, thus increasing the power. They are 
closed in reverse order, one after the other, as the load falls off. 

In the turbine shown in the picture, the valve mechanism can be 
seen at the middle, on top of the turbine Each valve controlling 
a passage to a nozzle has a vertical stem attached to a lifting lever. 
The free end of this lever has a roller that bears against a cam on 
a cam-shaft. The cam-shaft is under the control of the valve that 
is set in motion by the governor. As the load comes on, the cam¬ 
shaft is slowly rotated, and the cams on it are brought against the 
rollers on the lifting levers. As the cams are set at different angles, 
they come into action one after the other and so the valves are opened 
in the same order. 


42 







T-32 

This is a Curtis turbine set, with a rigid frame, having a capacity 
of 2000 kilowatts at 3600 revolutions per minute. It is constructed 
without a bed plate. 



T-33 

This view shows a horizontal Curtis turbine of the mixed pressure 
type. A mixed-pressure turbine is one that uses either high or 
low-pressure steam, or both. In this case, the low-pressure steam 
enters through the large pipe at the left, and the high-pressure 
steam through the emergency stop valve at the upper right. 

A mixed-pressure turbine is designed to take the exhaust steam 
from non-condensing reciprocating engines and use it to perform 


43 







work. The engine cannot use low-pressure steam economically; 
but it can use high-pressure steam economically. So, by combining 
a high-pressure engine and a low-pressure turbine, an economical 
unit is obtained. 

The governing mechanism is arranged so that all available low- 
pressure steam will be used, and then, if this is not enough to carry 
the load, high-pressure steam will be admitted to make up the 
necessary power. The row of eight high-pressure valves can be seen 
at the top. In front of them is the cam-shaft, the rotation of which 
opens the valves or closes them in succession. 

In some plants in which power is furnished by steam turbines, 
steam at low-pressure is needed for heating, drying, etc. In such 
cases, the turbines are designed to allow a part of the steam to be 
withdrawn after it has been expanded to a low-pressure through 
the earlier stages. This low-pressure steam is then used for the 
desired heating or drying, or while the remainder goes on through 
the remaining stages of the turbine. A turbine operated under 
these conditions is called a bleeder turbine. It is usually run con¬ 
densing, and is of the multi-stage type. 


44 



T-34 


Here is a view of the Interborough Plant of New York City, in 
which Curtis turbines of the vertical type are installed to use low- 
pressure steam from large reciprocating engines. In this plant the 
turbines were added to engines already installed. The economical 
full load of each engine was 5000 kilowatts. This load could be run 
up to as high as 8000 kilowatts, but at that overload the steam con¬ 
sumption became very high. By adding the turbines, the combined 
engine-turbine unit was able to carry 14000 kilowatts, with a steam 
consumption 20 per cent lower than the lowest for the engine alone. 
Each turbine has a capacity of 7500 kilowatts under full load. 

This picture gives a splendid idea of the saving of floor space by 
the use of turbines instead of engines. Compare the space taken 
by an engine of 5000 kilowatts capacity with the space taken by a 
turbine unit 50 per cent larger. 


45 







T-35 

This slide shows two vertical Curtis turbines of 5000 and 9000 
kilowatts capacity at 750 revolutions per minute, fitted with sur¬ 
face condensers. The steam pipes at its lower bend is fitted with a 
strainer, to prevent any solids from entering the turbine and clogg¬ 
ing the nozzles or damaging the vanes. The row of valves controll¬ 
ing the expansion nozzles can be seen at the front. The dry vacuum 
pump is at the left of the picture. 

In a turbine of this type, the wheels of the turbine are inside the 
larger part of the shell at the bottom, and the upper part encloses 
the generator. As the shaft is vertical, the weight of the rotor and 
the armature or revolving field is carried by a step bearing at the 
lower end of the shaft. A disk is doweled to the lower end of the 
shaft and rests on a similar disk forming the stationary part of the 
bearing. Oil under heavy pressure is forced up through a central 
hole in the stationary part, to a recess between the two disks, from 
which it flows out between them as the rotor turns. Thus, a film of 
oil is maintained between the rubbing surfaces and friction is avoided. 


46 












T-36 


Another vertical Curtis turbine of 5000 kilowatts capacity is 
shown here, fitted with a jet condenser. The steam passes first 
through a separator, then through a strainer, then through a throttle 
valve that is also an emergency valve, and then divides and goes to 
a group of high-pressure nozzle valves on each side of the turbine, 
under control of the governor. The connection to the condenser is 
short and direct. 


47 











T-37 


A small direct-connected Sturtevant generating set is shown in 
this view. The mechanism leading from the emergency governor 
on the end of the shaft to the steam stop-valve just below can be 
seen at the left. 



T-38 

This is the Westinghouse turbo-generator set of 100 kilowatts 
capacity. The single impulse wheel is inside the right-hand casing. 
This unit makes 300 revolutions per minute and is run non-condens¬ 
ing. 


48 











T-39 


This Terry 100-kilowatt turbo-generator set makes 2200 revolu¬ 
tions per minute and may be run either condensing or non-con¬ 
densing. It is used as an exciter in central stations, where it is 
generally non-condensing. In isolated plants it may be either 
condensing or non-condensing. 



T-40 


Another 100-kilowatt unit is here illustrated. It runs at 3600 
revolutions per minute and is used in lighting and manufacturing 
plants. The frame is rigid, and no bed plate is required. 

If the speed at which a machine turns is low, there is no danger if 
the rotating part is not perfectly balanced; but in steam turbines 
the rotative speed of the rotors is so great that a slight lack of 
balance is at once magnified into severe vibration, which, if con- 


49 









tinued, might damage the machine. For this reason, the rotors of 
steam turbines are very carefully balanced during manufacture. 
This balancing is not merely standing balance, but running balance 
as well. Standing balance is secured by resting the opposite ends of 
the rotor shaft on two parallel level rails and then adding or removing 
weights on one side or the other until there is no ‘ ‘heavy side” or 
“light side” to the rotor. In this condition of standing balance, it 
will rest in any position to which it is turned, on the rails. 

But standing balance alone is not enough. The balance must also 
be secured at the highest speed at which the rotor is to run. This 
balancing operation is much more difficult than the other, and re¬ 
quires more time and labor. Its success depends largely on ex¬ 
perience, and so it should not be undertaken by one who is not 
familiar with the method to be used. 

In operation, the turbine will be affected by severe vibrations if it 
gets out of balance. Thife unbalancing may arise from a number of 
things. The rotor may be perfectly balanced on leaving the shop, 
but may be damaged in transportation and so-be thrown out of 
balance. The breaking or stripping of some of the vanes may un¬ 
balance it. Unequal expansion, causing warping of the wheels or 
the shaft, may produce the same effect. 



T-41 

This is a Curtis 35-kilowatt set such as is used for isolated plants, 
for train lighting, and on shipboard. The bearings are lubricated 
by a pump geared to the shaft. 


50 






T-42 


A Westinghouse 10-kilowatt turbo-generator set is shown here. 
It has a single-stage impulse wheel, runs non-condensing, and 
makes 6000 revolutions per minute. 



T-43 


The rotating parts of the turbine set just shown is illustrated here. 
It shows the turbine wheel, the shaft, and the armature. The rings 
are oiling rings that hang down into oil pockets in the bearing 
pedestrals. As the shaft rotates, these rings turn and carry oil up on 
top of the shaft, from which point it flows down into the bearing. 


51 







T-44 

One of the most common uses of steam turbines is to drive centri¬ 
fugal pumps, because such pumps must be run at high speeds. 
This is a section through a three-stage pump, which is connected by 
the coupling at the right to the turbine. Each pump has a rotating 
part, called the impeller. The water enters at the lower left-hand 
end of the pump, and flows into the center of the first impeller, 
which, like the other two, is rotating at a high speed. The centri¬ 
fugal force set up throws the water outward into the curved casing, 
from which it flows under pressure to the next impeller. Here the 
same action occurs, and the water is delivered to the third stage at a 
higher pressure. It leaves the third stage at a still higher pressure, 
as each stage increases the pressure. 

When used as a boiler feed pump, the centrifugal pump usually 
has five stages, in order to build up the pressure. This style of 
pump has low efficiency, but the heat due to friction heats the 
water which enters the boilers, and so is not lost. An advantage 
of turbine-driven feed pumps is that the exhaust contains no oil, 
since the inside of a turbine is not lubricated; hence, the exhaust 
can be used in open feed water heaters. 


52 





T-45 


Here are two sectional views of the Alberger radial-flow impulse 
turbine. There are four nozzles spaced equally around the inside of 
the wheel. The vanes are at right angles to the wheel disk. The 
steam flows outward from the nozzles through the vanes, enters re¬ 
versing chambers and flows inward through the vanes, and then is 
reversed again and flows outward through the vanes, after which it 
is led away to the exhaust. The speed is governed by a throttling 
governor that alters the pressure of the steam admitted to the tur¬ 
bine, before it reaches the nozzles. 

Finally, the advantages of the steam turbine as compared, with 
the reciprocating engine may be summed up as follows: 

1. It is able to use highly superheated steam, and so its thermal 
efficiency is greater and its steam consumption is lower. 

2. Because of the high speed, a unit of given power weighs 
much less than an engine of equal power. 

3. Less floor space is required for a turbine; or, a greater amount 
of power can be developed with the same available floor space. 

4. The turbine uses no cylinder oil, and no more lubricating oil. 

5. There is a' saving in labor, as one engineer can care for more 
power in turbines than in engines. 

6. As the turbine is so carefully balanced, it requires less heavy, 
expensive foundations. 

7. The forces driving the rotor are steady and continuous, and 
so no flywheels are needed. 

8. A turbine will cary overloads more efficiently than an engine. 

9. The increase of steam consumption under light loads is smaller 
for the turbine than for the engine. 


53 


















































































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